Clinical testing involves performance of biochemical analysis or immunological analysis of proteins, sugars, lipids, enzymes, hormones, inorganic ions, disease markers, and the like in biological samples, such as blood or urine. Since clinical testing necessitates implementation of a plurality of testing items with a high reliability at high speed, a majority of such testing is performed with the use of an automatic analysis apparatus. Up to the present, for example, an automatic analysis apparatus that analyzes a reaction solution resulting from the reaction of a biological sample, such as serum, with a reagent of interest and measures the absorbance thereof to perform biochemical analysis has been known as a biochemistry automatic analysis apparatus. Such biochemistry automatic analysis apparatus comprises: a container that accommodates a sample and a reagent; and a reaction cell into which a sample and a reagent are introduced. The apparatus is composed of: a mechanism for automatically introducing a sample and a reagent into a reaction cell; an automatic agitation mechanism for mixing a sample and a reagent in the reaction cell; a mechanism for spectra measurement of the absorbance of a sample, which takes place during or after the reaction; and an automatic washing mechanism that suctions and discharges the reaction solution after the completion of the spectra measurement and washes the reaction cell.
In the field of automatic analysis apparatuses, reduction of the amounts of samples and reagents is a critical technical objective. As the number of items to be analyzed increases, specifically, the amounts of samples that can be used for each test item are reduced. Also, some samples are too valuable to prepare in large quantities. Thus, analysis of trace amounts of samples, which has been regarded as an advanced analytical technique in the past, has come to be performed on a routine basis. As the nature of analysis becomes advanced, reagents generally become expensive, and reduction of reagents is thus desired from the viewpoint of cost. Such reduction of the amounts of samples and reagents strongly motivate size reduction of reaction cells. Size reduction of reaction cells and reduction of the amounts of samples and reagents that are required for analysis are also advantageous in terms of, for example, improved throughput of the analysis and reduction of the amount of waste liquid.
In general, a reaction cell (which may be referred to as a “reaction container”) used for a common automatic analysis apparatus is made of a glass, synthetic resin, or the like. According to JP Patent Publication (kokai) No. 2005-30763 (A), for example, a material for a reaction cell is selected from among resin materials exhibiting low water absorption, low water vapor permeability, high total light transmission, a low refractive index, and a low mold shrinkage factor. A specific example of a preferable resin is a resin selected from among polycycloolefin resin, polycarbonate resin, acrylic resin, and polystyrene resin. JP Patent Publication (kokai) No. 2005-30763 (A) also refers to an objective for a reaction cell made of synthetic resin as reduction of the initial impedance of detection, such that air bubbles generated when a biological sample and a reagent are introduced into a cell would disadvantageously adhere to the cell inner surface and measurement could not be performed. This publication refers to low wettability of the cell inner surface as a cause of air bubble adhesion.
As effective means for improving wettability of the surface of general synthetic resin (also referred to as a plastic, polymeric resin, or polymer); i.e., means for hydrophilizing a surface, oxygen-plasma treatment, ozone treatment, ozone water treatment, corona discharge treatment, UV treatment, and other treatments are known. According to the Journal of Polymer Science: Part A: Polymer Chemistry, Vol. 26, 3309-3322, 1998, a surface of polyethylene, which is a type of polymeric resin, may be oxidized via corona discharge treatment to introduce peroxide at the surface, and a graft polymer may then be formed to modify the surface. Also, JP Patent Publication (kokai) No. 2000-346765 (A) reports the oxidation and hydrophilization of a plastic container via ozone treatment.
JP Patent Publication (kokai) No. 2007-183240 (A) reports that corona discharge treatment may be carried out in an atmosphere including oxygen such as air, in order to hydrophilize the limited area of the cell inner surface, which is close to a cell closure of a spectrum measurement wall for which air bubble adhesion is disadvantageous, and the upper region thereof on the cell inner surface, which is closer to the opening, can be maintained in a hydrophobic state. Since corona discharge treatment is carried out in an atmosphere including oxygen such as air, oxygen atoms are introduced onto the resin surface. Oxygen atoms are introduced onto the resin surface in the form of a hydroxyl group, ether group, carbonyl group, carboxyl group, or ester group. Among such functional groups, groups other than an ester group are hydrophilic functional groups. Accordingly, hydrophilic properties of the surface of resin that is originally highly hydrophobic are improved. Hydrophilic properties of the resin surface are measured in terms of a lowered contact angle against water. It is reported that the contact angle on a cell inner surface that has been subjected to corona discharge treatment in the above-described manner is reduced and hydrophilic properties are improved. It is also reported that the condition of oxygen atom introduction was confirmed based on the results of X-ray photoelectron spectroscopy measurement (hereafter referred to as “XPS”). Hydrophobic properties of the cell opening region prevent wetting of a reagent or sample, which in turn prevents mutual pollution of samples between reaction cells and improves data reliability. Such effects also contribute to reduction of the amounts of samples and reagents and also contribute to reduction of the running cost of the automatic analysis apparatus.
In JP Patent Publication (kokai) No. 2001-332238 (A), a decrease in the molecular weight of resin resulting from plasma treatment is pointed out as a problem to be solved, and inert gas (e.g., argon or helium) is reported as a preferable gas used for atmospheric plasma treatment. Also, Die Angewandte Makromolekulare Chemie: Vol. 120, 177-191, 1984, suggests that a nitrogen atom has three binding electrons and thus a nitrogen atom may cross-link carbon atoms after discharge. XPS is effective for analyzing the composition and the bonding state of a surface that has been modified in the above manner. Also, chemical modification techniques disclosed in Polymer, 1985, 26, 1162-1166 and Journal of Polymer Science: Part A: Polymer Chemistry, Vol. 26, 559-572, 1998, are available for analyzing the details of the surface bonding state. These techniques enable quantification of the amounts of a hydroxyl group, a carboxyl group, and the primary nitrogen (i.e., an amino group), which cannot be quantified via conventional XPS.